Measuring instruments, most notably those having a digital display of the measured parameter, typically "round up" to the higher of two successive display intervals any measured value which is greater than the midpoint of the two display intervals. A "breakpoint" is the point at which such rounding up is set to occur. For measured values less than the breakpoint, the lower of two successive intervals is displayed. For purposes of this discussion, when the breakpoints in a measuring instrument are set at the midpoint of successive display intervals, they are termed "generic breakpoints", and a weighing instrument employing generic breakpoints is termed a "scale". Such generic breakpoints, located at the midpoint of successive display intervals, are very typical and provide the least bias in measurement since they favor neither the higher or the lower display interval.
In certain applications, generic breakpoints are not well suited to a weighing instrument. For instance, when weighing mail it is important to know weight "up to" a postal rate break, such as one or two ounces. The same is generally true of packages, with respect to rate changes at integral pound intervals. Thus, in the United States, the breakpoints for a weighing instrument are set at, or just above the lower of two successive display intervals. (If set just above the lower interval, the offset is based on the maximum measuring error expected to be inherent in the weighing instrument.) In this manner, a mailpiece weighing 1.2 ounces, for instance, would register 2 ounces, for successive display intervals of "1" and "2" ounces. In practice, a postal weighing instrument displays weight in tenths of ounces, but the principle illustrated is still valid. For purposes of this discussion, when the breakpoints in a measuring instrument are set closer to one of two successive display intervals, rather than substantially at the midpoint thereof, they are termed "postal breakpoints", and a weighing instrument employing postal breakpoints is termed a "weight classifier". It should be noted that in certain countries other than the United States, the postal breakpoints are set at or near (within expected error) the higher of the two successive display intervals, since the postal rate structures are different.
The inventor has recognized that the bias inherent in the establishment of postal breakpoints at or near the lower (or higher) of successive display intervals, rather than at the midpoint thereof, may lead to a perceived discrepancy in the accuracy of the weighing instrument by a user accustomed to instruments employing generic breakpoints.
Thus, it is an object of this invention to provide a weighing instrument with breakpoints that are adaptive to the actual use or weighing history of the instrument.